An electrospinning process (ES process) is attracting attention as a technique that allows for relatively easy production of nanosized particles and fibers without using a mechanical or thermal force. A conventional ES process includes loading a solution of a nanofiber material into a syringe having a needle at its tip and jetting the solution from the needle while applying a high direct voltage between the needle and a collecting electrode. The solvent of the jetted solution evaporates instantaneously in the electric field, and the material is drawn by coulomb force while coagulating into a nanofiber, which deposits on the collecting electrode.
The above described conventional ES process is capable of producing only one or a few nanofibers from one needle. A technology for quantity production of nanofibers has not yet been established, and practical application of the ES process has made only slow progress.
ES processes described in Patent Literatures 1 to 5 below were proposed for increasing the nanofiber productivity. The ES process described in Patent Literature 1 includes providing a rotating conductive cylindrical container having a plurality of small openings with a polymer solution prepared by dissolving a polymer in a solvent, rotating the cylindrical container, thereby jetting the charged polymer solution from the small openings, drawing the jetted streams of the polymer solution into nanofibers by centrifugal force and electrostatic burst resulting from evaporation of the solvent, and deviating the nanofibers toward a second side of the axial direction of the cylindrical container by a repulsive electrode and/or an air blowing means disposed on a first side of the axial direction of the cylindrical container.
Patent Literature 1 discloses another ES process, in which an annular electrode is disposed to surround the lateral surface of a rotating conductive container having a plurality of small openings to provide a spinning space between the rotating container and the annular electrode. A polymer solution is fed to the container, and the container is rotated with a high voltage applied between the annular electrode and the vicinities of the small openings of the container to generate an electric field in the spinning space, whereby the polymer solution is jetted through the small openings and spun into charged fibers by centrifugal force and the action of the electric field. The fibers are drawn into nanofibers out of the spinning space by electrostatic burst associated with evaporation of the solvent.
According to the ES process disclosed in Patent Literatures 2 and 3, a solution of a polymer material is jetted from a metallic spinning nozzle with a high voltage applied between the nozzle and a metallic ball while a high speed air jet is directed perpendicular to the line connecting the metallic ball and the opening of the spinning nozzle, whereby the nanofiber spun from the nozzle is deviated and flown to the nanofiber collector where it is collected.
According to the ES process of Patent Literature 4, a resin-made nozzle is used to spray a spinning solution, a spinning solution is charged by an electrode, and the charged spinning solution is spray spun into an electric field. The container containing the spinning solution has, inside, an electrode made of a conductive material for charging the spinning solution.